w,h,n = 3.times.map { gets.to_i }
dp = {}
(1..w).each do |i|
    dp[i] = { includes: nil, excludes: nil }
end

n.times.map do
    s, k = gets.split.map(&:to_i) 
    (1..w).each do |i|
        if i == s
            (dp[i][:excludes] ||= []) << k
        else
            (dp[i][:includes] ||= []) << k
        end
    end
end


sum = dp.inject(0) do |s, (k,v)|
    if v[:excludes]
        s + h - (v[:excludes] - (v[:includes] || [])).uniq.size
    else
        s + v[:includes].uniq.size
    end
end

puts sum